Travel to Lhasa and other areas as an American living in Shanghai

I am planning a trip to Lhasa and the surrounding areas during the National Holiday the first week of October. I will be travelling with my girlfriend and her friend. They are both Chinese, but I am an American living in Shanghai. I will have a Chinese residency permit and a Z-Visa. My questions are what type of travel will we be allowed to do from Lhasa? Can we join independent travel groups that form in Lhasa or will we be required to travel with established tour operators? Can we travel with a travel group even though we are citizens of different countries? Also, what type of visa or documentation will be necessary in order to do this type of travel. Is an alien travel permit required for any travel outside of Lhasa? Do both Americans and Chinese need this type of travel permit? Thanks for your help.